Question

CaMn2O4 is of interest for use as a cathode in Ca ion batteries. Two structures can be

prepared the first is orthorhombic and is based on edge-sharing chains of MnO6

octahedra. The second is tetragonal and contains corner sharing MnO6 octahedra. The

volumes of the MnO6 octahedra are 11.82 and 8.89 Å3, respectively

a) Which of the two structures, orthorhombic or tetragonal, is likely to be stable at high

pressures?

Answer 1

a) High pressure favors the reduction of crystal volume, hence, tetragonal would be stable. Its volume is lower, since its crystal consists of octahedra with lower volume, than the orthorhombic phase.